1. Field of the Invention
The present invention relates to the magnetic resonance imaging (MRI) technology and, in particularly to an identification code circuit for a receiving coil in a magnetic resonance imaging system.
2. Description of the Prior Art
Magnetic resonance imaging is an imaging technology utilizing the magnetic resonance phenomenon. The basis of magnetic resonance phenomenon is that, for an atomic nucleus with an odd number of protons, such as the atomic nucleus of hydrogen which widely exists in the human body, the protons thereof have spin moments, just like a tiny magnet, and the spin axis of these tiny magnets normally has no regularity. If an external magnetic field is applied, however, the spin axis of these tiny magnets will be realigned by the magnetic field lines of the external magnetic field. In this state, by emitting radio frequency (RF) pulses with a specific frequency in order to excite the nuclei, these tiny magnets absorb a certain energy and resonance occurs, known as the magnetic resonance phenomenon. After stopping the radio frequency pulse emission, the excited atomic nuclei emit echo signals, and release the absorbed energy gradually as electromagnetic waves, and their phase and energy levels will return to the same state as before the excitation. The echo signals emitted by the atomic nuclei are further processed by spatial encoding, and an image can be reconstructed therefrom.
In a magnetic resonance imaging system, the pulses of the specific frequency are emitted to the atomic nuclei by a radio frequency transmitting coil, the echo signals emitted by the excited atomic nuclei are received by receiving coils. There is usually only one radio frequency transmitting coil, and depending on the site to be scanned there can be several receiving coils, which are also called local coils. A receiving coil can be inserted into a system socket by a system plug carried by itself, and the system plug connects the receiving coil to an identification code power supply of the system and ground respectively, then the receiving coil can be used normally, and the voltage of the abovementioned identification code power supply and the voltage of the internal resistance of the system power supply constitute together the total voltage of the system power supply. When scanning different parts of a human body, usually dedicated receiving coils are needed and they cannot be exchanged. This is because different receiving coils correspond to different specific parameters, such as scanning sequences, when the radio frequency transmitting coil works, how much power the radio frequency coil transmits and so on, so the use of a correct receiving coil can not only guarantee the quality of imaging, but also the safety of a patient, and it avoids the harm to the patient due to the excessive radio frequency absorption.
In order to ensure that the receiving coils are not to be mixed up, the best approach is to give each receiving coil a unique identification code, by which it can identify immediately among the receiving coils which is which. The simplest and most reliable way to realize such a unique identification code is to add a simple resistance circuit inside each receiving coil, so as to make different receiving coils correspond to different resistance values. Therefore, when a receiving coil corresponding to a different resistance value is connected into the system, the voltage of the receiving coil assigned by the identification code power supply of the system will change based on the different resistance value of the above resistance circuit, thereby realizing the identification of different receiving coils, and the above voltage assigned to each receiving coil is the identification code of that receiving coil.
For an ordinary receiving coil with an independent system plug, the realization of the above resistance circuit is very easy, but sometimes for the sake of cost saving, structure simplification, or for carrying out special scanning by a combination of several receiving coils, some of the receiving coils do not have independent system plugs, therefore such receiving coils cannot be connected to the system directly, and instead they must be connected to other receiving coils with independent system plugs, so as to realize the indirect connection into the system. The aforementioned receiving coils without independent system plugs are called sub-coils, and the receiving coils with independent system plugs are called main coils. Such a sub-coil usually comprises a coil plug, the main coil has a corresponding socket, the connection of the sub-coil to the main coil is realized by the insertion of the coil plug of the sub-coil into the corresponding socket of the main coil, and the combined two receiving coils will be identified by the system using one identification code.
The combination of the sub-coil and the main coil sometimes can be very complicated, such as a head receiving coil is the main coil. Another neck coil is the sub-coil, and these two receiving coils share one independent system plug connection system of the main coil; and assuming that the head receiving coil comprises the upper and lower two parts, and the neck receiving coil also includes the upper and lower two parts, so that the combination of these two receiving coils comprise multiple possibilities, such as the lower part of the head and the lower part of the neck, the whole head and the lower part of the neck, the lower part of the head and the whole neck, the whole head and the whole neck, etc. In order to distinguish the above different use conditions, an identification code will have to be set for each condition, and then the situations for the identification codes become very complicated.
In order to solve the above problem of complicated identification codes caused by the combinations of the sub-coil and the main coil, the following two solutions are known in the prior art.
In the first known solution, independently of the sub-coil or the main coil, each of the receiving coils is provided with an independent system plug, so the realization of the identification code is relatively simple, namely a resistance circuit is set up inside each receiving coil, so that different receiving coils correspond to different resistance values. Therefore, when the receiving coil corresponding to a different resistance value is connected to the system, the voltage of the receiving coil assigned by the system will be different, thus realizing the identification of the different receiving coils.
Although this solution is simple to implement, due to the high costs of the system plugs, the increase in the number of the system plugs is equivalent to the increase of the production costs of the receiving coils, and also the system needs correspondingly more sockets to meet the needs of the increased number of system plugs, thus leading to greatly increased system costs.
In the second solution, oscillating circuits are designed for the sub-coil and the main coil, and independent power supplies are created by using the oscillating circuits (such a power supply can be a negative power supply), after the main coil and sub-coil are connected into the system, the voltage generated by the independent power supply are added on top of the voltage of the identification code power supply, which will generate a different superposed voltage, and the system identifies the different combinations of the main coil and the sub-coil by the different superposed voltage values. In this case, the aforementioned different superposed voltage values are the identification codes corresponding to different combinations of the main coil and the sub-coil.
Although this method still allows the sub-coil to be connected to the system via the main coil and it saves costs, the design of the oscillating circuit itself is quite complicated. Currently, regarding the combination of the sub-coil and the main coil, there is not yet a solution that is not only cost-effective but also simple in realizing the generation of the identification codes.